A conventional switch device of this type is shown in FIG. 4, and comprises a switch 10 having a lock mechanism and a second switch 20 acting to unlock the switch 10. When the push member of the switch 10 is depressed to a certain depth, one contact is switched to another. Simultaneously, the switch 10 is locked. Once the switch 10 has been locked, the push member is maintained locked in the depressed position even if the depressing force is no longer applied to the switch 10. With respect to the switch 20, when the push member is depressed, one contact is switched to another. When the push member of the switch 20 is pushed and released to its original height, the switch 20 unlocks the switch 10 from its depressed position.
The switch 10 comprises the push member, indicated by numeral 11, a cam 12 formed on a part of the push member 11, a common terminal 13, switched terminals 14, 15, and a clip 16 that moves between the terminals 14 and 15 and acts as a movable contact. The push member 11 is mounted in a chassis 40 such that the cam 12 and the clip 16 can move a distance corresponding to the amount of depression. The clip 16 serves in such a way that when the member 11 is not depressed, the common terminal 13 is connected with the terminal 14, while when the member is depressed, the common terminal 13 is connected with the terminal 15.
The switch 20 comprises the push member, indicated by numeral 21, a heart cam 22 formed at an intermediate location on a lower part of the member 21, a reset pin 23, a retainer 24 that holds the pin 23, a common terminal 25, switched terminals 26, 27, a clip 28, and a coiled spring 29 for biasing the push member 21 back to its original position. The member 21 moves the cam 22 and the clip 28 simultaneously so that the reset pin 23 may move in a circular path within the cam 22. Also, the member 21 connects the common contact 25 with the terminal 26 or 27. A knob (not shown) is installed on the top of the push member 21. Both ends of the pin 23 are bent at right angles toward the push member 21. One of these ends is fixed to the retainer 24, which is affixed to the chassis 40. The other end is rotatably placed in the path of the cam 22.
A lock plate 41 is disposed between the switches 10 and 20, and has U-shaped cutouts located below the push members 11 and 21. The cutouts engage the surface of the cam 12 and the surface of the pin 23, respectively. The lock plate 41 is biased to the left as viewed in the figure by a spring 42. The operation of the conventional switch device constructed as described above is described below by referring to FIGS. 4-6.
FIG. 4 shows the condition in which the push member 11 of the switch 10 is depressed, so that the switch is locked in the depressed position. The push member 21 of the switch 20 is not operated. Under this condition, if the push member 21 of the switch 20 is depressed, the heart cam 22 is lowered as shown in FIG. 5. Thus, the lower end of the reset pin 23 is located near the top of the cam 22. Also, the clip 28 connects the common terminal 25 with the terminal 27.
Where the switch device is used for a telephone set, when an external call is received, the switch 10 is depressed. Then, if this call is to be transferred to another interphone, the push member of the switch 20 is depressed to suspend the call. Then, the finger is moved away from the push member 21 of the switch 20 and, at the same time, the switch 10 is unlocked from the depressed position. Then, the switch 20 is returned to its original state. In this way, this telephone set is disconnected from the telephone circuit. FIG. 4 shows the condition in which this telephone set is connected with the external line. FIG. 5 shows the condition in which the external call is suspended.
Under the condition shown in FIG. 5, if the operated member 21 ceases to be depressed, the heart cam 22 and the clip 28 move up together with the operated member 21 as shown in FIG. 6. During this process, the pin 23 drops into the right recess in the cam 22 from the top end, permitting the pin 23 to rotate to the right. Then, the lock plate 41 shifts to the right against the biasing force of the spring 42. As a result, the cutout moves away from the cam 12. Thus, the push member 11 is unlocked. Then, the member 11 is allowed to be moved upward by a spring (not shown) mounted on the member 11. Concurrently, the clip 16 is elevated with the result that the contact 14 is connected with the common contact 13. Under this condition, the telephone set equipped with this switch device is disconnected from the telephone circuit. In the conventional telephone line-switching device designed as described above, the switch 10 cannot be unlocked before the switch 10 is operated to perform a switching operation. For this purpose, the structure of the switch device is made complex. More specifically, the cam 12, the heart cam 22, the reset pin 23, etc. are required to be provided to permit the plural switches to interlock.